Embodiments of the present invention generally relate to digital watermarking. Digital watermarks can be applied to image content, moving (video) or stationary (still pictures). These watermarks can serve a variety of purposes, including the tracking of unauthorized copies back to the party who licensed the use of the content and who was responsible for preventing its further distribution.
There are several watermarking techniques for images/video, covering a wide range of properties. These techniques are generally applicable in the pixel domain, i.e., they can insert watermarks in the raw (uncompressed) images.
In practice, video is usually compressed before being distributed on a physical medium (e.g., DVD) or over a network (e.g., soft copy downloadable over the Internet). If the watermark payload is different for every copy and the watermark is applied in the pixel domain, then each individual copy needs to be compressed, since it is different from every other copy. This concept is illustrated in FIG. 1. Compression can be a very expensive operation both from a computing resource standpoint (it requires a lot of computational power) as well as from a human resource standpoint (it is very common to have a human inspect the results of the compression algorithm and adjust parameters to improve the visual result). The cost of the per-copy operations renders the watermark insertion in the pixel domain untenable for these applications.
For watermarking of material already in the compressed domain (e.g., DVDs, Internet downloads), it is important that the watermark embedding process does not result in extensive changes in the bitstream, because this could undermine compression choices made at the time of the initial encoding both to optimize the perceived quality of the encoding, and to maintain rate control, bit-rate, and other profile constraints of the intended application.
Therefore, there is a need in the art for watermarking content in the compressed domain. There is also a need in the art for inserting a watermark in the compressed domain with minimal change to the bitstream.